Field of the Invention and Description of the Prior Art
This invention relates to an improved snowmobile suspension system and it particularly relates to an improved rear suspension system for supporting a snowmobile frame and a support assembly for a snowmobile drive belt, relative to each other.
It is well known that practically any land vehicle uses a suspension system between the body or frame of the vehicle, used to support a rider or riders, and the portion of the vehicle which supports the ground engaging parts, such as wheels or a continuous drive belt or track of a vehicle. This is true of automobiles, trucks, motorcycles, and the like. The present invention is specifically directed towards a suspension system used for supporting the frame or "tunnel" of a snowmobile, on which a rider sits, relative to the frame or support which operatively carries a continuous drive belt or drive track that propels the snowmobile. Known suspension systems for snowmobiles are shown in the prior art, for example, in Swenson Pat. No. 3,485,312; Skime Pat. No. 3,690,394; and Olson Pat. No. 3,931,861.
Generally speaking, there are two types of snowmobiles suspension systems, one being the slide rail type, such as, for example, shown in the Swenson Pat. No. 3,485,312, mentioned above, and the wheel type of support assembly. The present invention is directed to the rear suspension for a slide rail type of snowmobile suspension system.
The slide rail type of suspension system is considered the most popular type of suspension system for snowmobiles, because it provides for better performance, ride and stability. There are a wide variety of variations of slide rail suspension systems, but all involve the common feature of having the suspension system slide over the track surface rather than roll over the surface as found in the wheel type of suspension system. In some types of slide rail suspension systems, one or more pairs of wheels are mounted on the slide rail in order to reduce the force on the slide rail surface so as to reduce the wear of the slide member.
In recent years, there has been an increasing interest and emphasis on the trail riding usage of snowmobiles. Many users of snowmobiles, however, are not entirely satisfied with the quality of the ride provided by their snowmobiles. There are a variety of reasons for an unsatisfactory ride, but generally the unsatisfactory ride results from poorly maintained trail surfaces and from limitations in the conventional snowmobile suspension designs. Thus, although snowmobile suspension systems have been generally satisfactory, with increased usage of snowmobiles and with the need which has arisen to provide for an improved "ride", an improvement in the snowmobile suspension system is called for.
The major factors in a snowmobile design that affect ride quality include the spring rate or stiffness of springs used for the suspension system, the use of velocity sensitive shock absorbers in the suspension system, the vertical travel between the snowmobile frame or tunnel and the support frame for the track support, and the static deflection of the snowmobile. In order to provide for an improved ride, the rear suspension system calls for a softer or lower spring rate for the springs that cooperate to suspend the snowmobile frame relative to the drive track support and an increase in the vertical travel between the snowmobile frame and track support. The common maximum vertical travel is, at present, approximately four inches. The primary limiting factor in the current snowmobile suspension systems is that the ride rates, that is, the vertical spring rate component, decreases as the deflection between the frame and the track support increases. For this reason, high initial spring rates are required in order to preclude frequent bottoming of the snowmobile frame relative to the track support, particularly when the snowmobile is traversing bumpy terrain.